A new blue light-emitting terphenyl-bridged bisbenzimidazolium salts: Synthesis, crystal structure, and photophysical properties

Eight novel terphenyl-bridged bisbenzimidazolium salts bearing N-alkyl side chains were synthesized by alkylation and quaternization of terphenyl-bridged bisbenzimidazoles with excess alkyl bromides, using sodium carbonate as the base in N,N-dimethylformamide solution. The bisbenzimidazolium salts showed good solubility in water and common organic solvents, such as dichloromethane, chloroform, methanol, acetonitrile, and N,N-dimethylformamide. They emitted violet-blue light (λ_max^Em≈397-400nm) with fluorescence quantum yields of 0.65-0.78 in aqueous solution, whereas they emitted blue light (λ_max^Em≈420-441nm) in thin films. The photoluminescent properties and crystal structure of the bisbenzimidazolium salts have been investigated.